Hydrolyzable polysiloxane-polyoxyalkylene block copolymers, namely those copolymers wherein the polysiloxane and polyoxyalkylene blocks are linked by hydrolytically unstable silicon-oxygen-carbon bonds, have found wide acceptance as foam stabilizers in the production of polyurethane foam. They are produced, inter alia, by the reaction of a polyoxyalkylene alcohol with a polysiloxane containing a halogen atom directly attached to a silicon atom of the polysiloxane, as shown by the following skeletal equation: EQU .tbd.SiCl+HOC.tbd..revreaction..tbd.SiOC.tbd.+HCl
Typically, the reaction is carried out by mixing the halopolysiloxane with the polyoxyalkylene alcohol in the presence of a solvent such as toluene and in the absence of a catalyst. Since the reaction produces by-product hydrogen halide (e.g., hydrogen chloride) that is in equilibrium with the desired product and the reactants, a means must be provided for driving the reaction to completion. One method of driving the reaction to completion encompasses the neutralization of the hydrogen halide with a base. By way of illustration, U.S. Pat. No. 3,115,512 discloses the neutralization with a base of the hydrogen halide by-product of the reaction of halopolysiloxanylsulfates with organic hydroxyl-containing compounds (including polyoxyalkylene alcohols) in the process of producing "silicic acid esters" (including polysiloxane-polyoxyalkylene block copolymers). Suitable bases disclosed in that patent include metal hydroxides and their alkoxy derivatives such as sodium methylate, ammonia, amines and pyridines. As a further illustration, U.S. Pat. No. 3,532,732 discloses the neutralization with ammonia of the hydrogen chloride by-product of the reaction of chloropolysiloxanylsulfates with polyoxyalkylene derivatives in the presence of a toluene solvent in the process of producing polysiloxane-polyoxyalkylene block copolymers. The processes disclosed in the above-mentioned patents involve the formation of a halide salt by-product. Separation of this salt from the block copolymer product is difficult, time consuming and expensive.